The invention relates to a device and a method for calibration of a mass flow sensor. The device is occasionally also referred to as a flow bench.
The combustion process in an internal combustion engine depends quite decisively on the amount of air that is supplied. Therefore, mass flow sensors which sense the mass of a flowing gas are used. The sensed measuring signal in the form of a current and voltage value or a period duration value in the case of clocked signals is subsequently assigned a value for the mass flow, for example in kilograms/hour. In order that the sensed measuring signals correctly reproduce the mass flowing past, it is necessary to calibrate the mass flow sensor.
DE 198 57 329 A1 discloses a flow bench and a method for the testing and calibration of a mass flow sensor. In the case of the flow bench, a mass flow sensor to be calibrated and a reference mass flow sensor are arranged one behind the other in a flow channel. A pump generates an air mass flow in the flow channel, the two mass flow sensors being positioned upstream of a throttle valve. A position downstream is also possible. A controller sets the throttle valve in the flow channel, so that the mass flow varies in intensity. The measured values of the reference mass flow sensor are used to determine the values for the mass flow sensor to be calibrated. In the determination of the values for the mass flow sensor to be calibrated, pressure losses at the upstream sensor must be taken into account.
In the not yet published German patent application DE 101 49 292.8, a description is given of operating without a reference mass flow sensor. In this case, a mass flow/time profile is preset in the flow channel by means of a standard valve. The mass flow sensor to be calibrated is calibrated in the air mass flow set by the standard valve on the basis of a predetermined mass/time profile. A disadvantage of this method, also referred to as masterless calibration, is that the temperature and pressure profiles on the suction side of the pump must be kept absolutely constant. Any changes caused by the ambient temperature and/or the ambient pressure may falsify the values of the calibration.